INTERACTIVE EFFECTS OF FEED-INTAKE AND STAGE OF GROWTH ON THE LYSINE REQUIREMENT OF PIGS

We studied the effect of reduced feed intake on the lysine requirement of pigs at the early growing (G) and finishing (F) phases. Two sets o f 40 individually penned crossbred barrows averaging 27.1 +/- 2 (G) an d 92.6 +/- 1.1 kg BW (F) were fed five dietary treatments (G;.75,.90, 1.05, 1.20, 1.35%; and F:.45,.60,.75,.90, 1.05% lysine) at two feeding levels (equivalents to 100 and 80% ad libitum intakes) for 15 d. In b oth stages pigs on the 80% feeding level had lower ADG (P <.001) and l ower plasma urea nitrogen (PUN) concentrations (P <.10) than pigs on t he 100% feeding level. In all instances, increasing dietary lysine cau sed ADG to increase (P <.05) and PUN to decrease (P <.10) linearly. A tendency for an interaction was detected between the effects of growth stage and the effects of feeding level on the lysine requirements est imated by ADG (P <.19) and PUN (P <.10). In the F stage, pigs on the 8 0% feeding level required a greater dietary lysine concentration to ma ximize ADG and minimize PUN (.85 and.87%, respectively) than pigs on t he 100% feeding level (.61 and.68%, respectively). In the G stage, how ever, the dietary lysine concentrations required to maximize ADG (.97 to 1.01%) and minimize PUN (1.05 to 1.09%) were not different (P >.20) between feeding levels. We conclude that the effect of a reduction in feed intake on the lysine requirement depends on the stage of growth of the pigs.